The present invention relates to golf balls and, in particular, to polymeric compositions useful in golf ball covers, cores, and intermediate layers between the cover and the core. The polymeric compositions include at least one anionic polymer which has neutralizable hydroxyl and/or dealkylable ether groups, at least a portion of which are neutralized by a metal ion to provide anionic groups attached to the polymer.
Three-piece, wound-core golf balls with balata (trans-polyisoprene) covers are typically preferred by professional and low handicap amateur golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and thus lacks the durability required by the average golfer.
Two-piece golf balls, which are typically used by the average amateur golfer, provide a combination of durability and maximum distance that is not available with balata covered balls. These balls comprise a core, formed of a solid sphere which typically comprises a polybutadiene-based compound, encased in an ionomer cover, such as SURLYN(copyright). Golf ball cover ionomers are, typically, copolymers of an olefin and an unsaturated carboxylic acid in which at least a portion of the carboxylic acid groups have been neutralized with a metal ion, typically sodium or zinc. These balls are extremely durable, have good shear resistance, and are difficult to cut. However, this durability results from the hardness of the ionomer, which gives such balls a very hard xe2x80x9cfeelxe2x80x9d when struck, which many golfers find inferior to the softer xe2x80x9cfeelxe2x80x9d of a balata covered ball. In addition, the hardness of the ionomer gives the balls a lower spin rate, making these balls more difficult to control.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball, and the durability of an ionomer covered two-piece ball. These attempts have focused largely on modifying the properties of ionomer compositions by forming ionomer blends.
For example, U.S. Pat. Nos. 4,884,814, 5,120,791, 5,324,783, 5,415,937 and 5,492,972 disclose ball compositions which are blends of high-hardness ionomers and low-hardness ionomers. Other patents disclose blends of ionomers and nonionic polymers, such as U.S. Pat. Nos. 5,397,840, 5,516,847, 5,703,166. These patents attempt to overcome the inherent immiscibility of ionomers and nonionic polymers by adding polar functionalities to the nonionic polymers (see, e.g., U.S. Pat. Nos. 4,986,545 and 5,359,000), or by adding compatibilizers to provide or enhance the compatibility of the two polymer species (see, e.g., U.S. Pat. Nos. 5,155,157 and 5,321,089, and Japanese patent application 6,192,512 (1994)). Still other patents disclose blends of normally immiscible or poorly miscible non-ionomer polymers with compatibilizers (see, e.g., U.S. Pat. No. 5,422,398).
U.S. Pat. No. 4,526,375 discloses golf balls having improved low temperature impact resistance including a cover composition having an ionic polymer with at least two different metal ions in one molecule.
U.S. Pat. No. 5,692,974 discloses compositions using cationic polymers having positively charged quaternary ammonium groups. The cationic groups, preferably present in cationic polyurethane polymers, impart improved characteristics to golf ball covers formed therefrom.
Notwithstanding these efforts, there is no known prior art disclosure of the use of anionic polymers having anionic groups derived from other, non-carboxylic acid, neutralizable moieties, such as hydroxyl and dealkylable moieties, such as ether groups, to form golf balls. Such anionic polymers would have desirable hydrogen bonding or dipole interactions as well as ionic interactions which can be utilized to impart improved characteristics to golf ball cores, covers, and intermediate layers, such as improved durability and resiliency.
Thus, there has now been discovered surprisingly improved golf ball-forming compositions comprising anionic polymers having anionic moieties derived from neutralizable hydroxyl and/or dealkylable ether groups, which, when used to form golf balls, produce balls which unexpectedly remedy the deficiencies of the prior art materials discussed above.
The present invention is directed to golf balls comprising a cover, a core, and optionally one or more intermediate layers disposed between the cover and the core, wherein at least one of the cover, the core and, if present, the intermediate layer or layers, comprises an anionic polymer having neutralizable hydroxyl and/or dealkylable ether groups, wherein the golf ball has a coefficient of restitution of greater than about 0.7 and a compression of at least about 50, the cover has a thickness of at least about 0.03 inches and at least about 60 percent dimple coverage, and the anionic polymer has a flexural modulus from about 500 psi to 300,000 psi, a hardness of at least about 15 Shore A, a specific gravity of at least about 0.7, a dynamic shear storage modulus of at least about 104 dyn/cm2, and a loss tangent of less than about 1 at about 23xc2x0 C. At least a portion of the neutralizable or dealkylable groups are neutralized by a metal base to leave anionic moieties attached to the polymer.
The anionic polymer comprises repeating units of formula (Ia): 
wherein R1, is OH, OC(O)R5, Oxe2x88x92M+V, (CH2)nRb, (CHRz)nRb, or aryl, wherein n is at least 1, R5 is a lower alkyl, M is a metal ion, V is an integer from 1 to 5, Rb is OH, OC(O)R5, Oxe2x88x92M+V, and Rz, is a lower alkyl or aryl, R2, R3 and R4 are each independently selected from the group consisting of hydrogen, straight-chain or branched-chain lower alkyl, and substituted alkyl in which one or more hydrogen atoms is replaced by a substituent selected from the group consisting of COOH, SO3H, NH2 or a lower alkyl substituted or di-substituted amine, halogen, OH, SH, silicone, and lower alkyl ether.
In a preferred embodiment, the anionic polymer is a copolymer of substituted or unsubstituted ethylene and substituted or unsubstituted vinyl alcohol, acetate, p-hydroxy styrene, or p-methoxy styrene. Thus, in this embodiment, the anionic copolymer is a random, block, or alternating copolymer of units (Ia) and (Ib), where units (Ib) have the formula 
wherein R6, R7, R8 and R9 are each independently selected from the group as defined above for R2. In a preferred embodiment, each of R2, R3, R4, R6, R7, R8 and R9 is hydrogen. In another preferred embodiment, R5 is methyl.
In one embodiment, the units Ia are present in amounts from about 1 to 99 weight percent and units Ib are present in amounts from about 99 to 1 weight percent.
In a more preferred embodiment, the anionic polymer is a copolymer of ethylene and vinyl alcohol, vinyl acetate, i.e., R1, is OH or OC(O)CH3, p-hydroxy styrene, or p-methoxy styrene, and the remaining R groups are hydrogen.
In another embodiment, the anionic polymer is a copolymer or terpolymer of formula (II): 
wherein:
R1-R9 are each independently selected from the groups defined above;
R10-R12 are each independently selected from the group as defined above for R2; and
R13 is OH or OC(O)R14, where R14 is a lower alkyl;
the remaining R groups are each independently selected from the group consisting of hydrogen, straight-chain or branched-chain lower alkyl, and substituted alkyl in which one or more hydrogen atoms is replaced by a substituent selected from the group consisting of COOH, SO3H, NH2 or a lower alkyl substituted or di-substituted amine, halogen, OH, SH, silicone, lower alkyl ether, and lower alkyl ether;
x ranges from about 99 to 50 weight percent of the polymer, y ranges from about 1 to 50 weight percent of the polymer, and z ranges from about 0 to 50 weight percent of the polymer; and
wherein at least a portion of the neutralizable groups are neutralized with a metal ion.
The anionic polymers of the present invention can be mixed with one or more additional ionic and non-ionic polymers, present in an amount of about 1 to 99 percent by weight, preferably about 5 to 80 percent, based on the total weight of the anionic polymer and the additional polymer. Preferred additional polymers include polyvinyl alcohol or a copolymer of ethylene and vinyl alcohol, styrene-allyl alcohol, or ethylene-allyl alcohol copolymer.
In a preferred embodiment, the anionic polymer has a flexural modulus of from about 2,000 to 200,000 psi. In yet another embodiment, the metal ion is an ion of an alkali metal, an alkaline earth metal, a transition metal, a Group III metal, or a Group IV metal. In a preferred embodiment, the alkali metal is lithium, sodium or potassium; the alkaline earth metal is magnesium; and the transition metal is titanium, zirconium, tungsten or zinc.
In one optional, but preferred, embodiment, the at least one intermediate layer is disposed between the cover and the core. In another optional, but more preferred embodiment, said intermediate layer is formed of a composition which comprises an anionic polymer having at least one of a neutralizable hydroxyl or dealkylable ether group, and at least a portion of the neutralizable or dealkylable groups are neutralized with a metal ion.
In one embodiment, the core contains at least one solid, hollow, or fluid portion. In another embodiment, at least one of the intermediate layers includes a tensioned elastomeric material. In yet another embodiment, at least a portion of at least one of the core, the at least one intermediate layer, and the cover is foamed, comprises a density-modifying filler, or both.